Porous barrier media find application in a number of areas including liquid sampling and transfer apparatus, such as pipettes. Barrier media are often incorporated into liquid sampling and transfer apparatus to prevent contamination of the apparatus in situations where the liquid is overdrawn by human or mechanical error.
In addressing apparatus contamination, porous barrier media have incorporated absorbent materials which are operable to seal the pores of the media when exposed to liquid. The self-sealing nature of the barrier media comprising absorbent materials inhibits or prevents liquid from traveling through the media and contaminating downstream apparatus. In the sealed state, barrier media comprising absorbent materials additionally inhibit or prevent the flow of gasses thereby requiring replacement of the media for further liquid transfer or sampling.
In addition to absorbent materials, barrier media have been coated with metal salt color changing species, such as cobalt chloride. The coating of metal salt color changing species onto barrier media facilitates a determination of when the media has been contacted by fluid.
Several problems, however, exist with metal salt color changing species. Cobalt chloride, for example, is very sensitive to moisture and must be stored under extremely dry conditions in order to prevent color change before use. Moreover, the color change indication of cobalt chloride is slow leading to a delayed response upon contact of barrier media by a liquid. Many metal salts, including cobalt chloride, are toxic and, therefore, cannot be used in biological applications. Furthermore, metal salts coated onto porous barrier media can be displaced from the porous media and contaminate the liquid sample.